The long-term objective of this project is to provide scientists with a practical instrument that can be used in obtaining quantitative high resolution images of dissolved oxygen concentration in tissue. Such instruments could be used to develop understanding of the normal distribution of oxygen in diverse tissues and to understand how the distribution may change during pathological ischemia (e.g. stroke, heart attack, etc.). Additionally, it is hoped that the new instrument can be used in pre-clinical screening (in animal models) of drugs for use in the treatment of medical conditions in which changes in the concentration of dissolved oxygen is important. The objective of Phase I is to develop a prototype instrument of one that can be provided commercially for use by research scientists to image the distribution of dissolved oxygen. The techniqueemployed will find oxygen from the phosphorescence lifetime of known extracellular probe molecules. The planned work makes use of a non-commercial pioneering instrument as a starting point. Goals of Phase I include increasing the sensitivity of the instrument while increasing the speed of image processing, to provide a user- friendly computer interface and to lower the cost of the final product. In Phase II, "Real time" oxygen maps would be added to the system's capability through additional software development. The spatial resolution and sensitivity of the system would be measured in vivo for a preparation requiring high resolution (e.g. cerebral cortex) and optimized. Development of appropriate new phosphorescence probes would be contracted out. The capability to image other appropriate substances (pH, Ca2+, etc.) would be added.